EP2659747B1 - Circuit arrangement and method for operating at least one high-pressure discharge lamp - Google Patents

Description

Technical area

The present invention relates to a circuit arrangement for operating at least one high-pressure discharge lamp with a voltage converter having at least one electronic switch, a drive circuit for driving the at least one electronic switch of the voltage converter with a predeterminable converter frequency, a first and a second connection for coupling to the at least one high-pressure discharge lamp, a first capacitor coupled between the voltage converter and the first terminal for the discharge lamp, and a charging device coupled to the first capacitor for charging it with a DC voltage to an ignition voltage for igniting the high pressure discharge lamp. It also relates to a corresponding method for operating a high-pressure discharge lamp.

State of the art

High-intensity discharge lamps have arc resonances, so-called acoustic resonances, in operation in certain frequency ranges. These resonance frequencies are usually in a range between 1 kHz to 1 MHz. Therefore, these lamps are usually operated with a square wave frequency below 1 kHz. Electronic ballasts designed to have such a square frequency However, to provide, but are technically very complex and therefore corresponding bulky and expensive.

The advantage is the operation in the area around and above 1 MHz. However, there is the problem that the impulse superposition ignition used in the rectangular operation can not be used due to the high inductance of the pulse transformer in HF operation. Namely, such a pulse transformer acts as a filter for the high frequencies and thereby limits the transmission of the current in these frequency ranges. With such high frequencies, virtually no current flow through such a pulse transformer is made possible. So you have to look for other ignition alternatives.

From the DE 199 09 530 A1 In this context, a circuit arrangement is known which enables DC ignition of a high-pressure discharge lamp. In this case, an ignition or coupling capacitance, which is designated there by C1, to the ignition voltage, which may be, for example, between 10 and 15 kV, charged. For stationary operation of the high-pressure discharge lamp, however, this ignition or coupling capacitance must have a very high capacitance value in order to transmit the corresponding current for the required lamp power. In conjunction with the high dielectric strength for the ignition, this results in very voluminous and expensive capacitors. In the ignition process, this capacitor is namely the ignition capacity, which is charged to the appropriate ignition voltage, while in stationary operation of the lamp this capacitor forced - works as a coupling capacity. This means that this capacitor must be the circuit between the transformer close the voltage converter and the lamp and thus take over the entire lamp current and forward. Through the inductance L1 and the capacitor C3, see there Fig. 2 , only the take-over voltage is provided, which is only a few kV and thus significantly below the ignition voltage.

Transducers for electronic ballasts for high frequency operation are generally operated in resonance mode. In this case, the transistors for loss of power reduction in the current or de-energized state, that is at zero crossing. For this purpose, an additional resonance capacitor is necessary on the primary side of the converter, which forms a resonant circuit with the primary inductance. In the case of resonance, the voltages or currents are sinusoidal, so that can be switched at zero crossing. In this context, reference is made to the WO 98/18297 A1 in which the resonance capacitor is designated C2. The primary inductance is formed by the windings W1a and W1b of the push-pull converter, which in turn comprises the transistors T1, T2 and the transformer Tr1.

Presentation of the invention

Therefore, the object of the present invention is to develop a circuit arrangement mentioned at the outset or an initially mentioned method such that the capacitance of the first capacitor, which constitutes the coupling or ignition capacitor, can be reduced.

This object is achieved by a circuit arrangement having the features of patent claim 1 and by a method having the features of patent claim 15.

The present invention is based on the finding that this is fundamentally made possible when the voltage converter comprises a transformer, wherein the transformer comprises a primary inductance with at least one first and a second terminal and a secondary inductance with a first and a second terminal, wherein the first capacitor is coupled between the first terminal of the secondary inductance and the first terminal for the at least one high-pressure discharge lamp. According to the invention, the converter frequency in stationary operation of the circuit arrangement is selected such that the secondary side, which comprises at least the series connection of secondary inductance, first capacitor and high-pressure discharge lamp, is operated substantially in resonance. Due to the fact that the inductances and capacitances of the series circuit with the high-pressure discharge lamp form a series resonant circuit in which the impedances of the components assume very small values in the case of resonance, the impedance of the ignition or coupling capacitor, that is of the first capacitor, is also in operation with such Converter frequency very small. As a result, at relatively low frequencies and low capacities - compared without resonance - a high current can be passed. This is also sinusoidal. As a result, the capacity of the first capacitor compared to the known procedure can be significantly reduced. This is a cost reduction of the first capacitor and a reduction in volume the circuit arrangement, that is the electronic ballast, accompanied. Moreover, the components of the voltage converter can also be made smaller, which leads to a further cost reduction.

The invention is not to be confused with the parallel to the lamp resonant capacitor C1 WO 98/18297 A1 or the capacitor C2 of the DE 199 09 530 A1 , Which provide a far above the stationary frequency of the voltage converter further resonance point for voltage overshoot for the adoption of the high-pressure discharge lamp and are ineffective in stationary lamp operation, since they are short-circuited by the high pressure discharge lamp. Their capacity value is much smaller than the ignition or coupling capacity.

Furthermore, the present invention provides the advantage that the resonance capacitor of the primary side as in WO 98/18297 A1 still present, can be omitted, since the primary current is now also forcibly sinusoidal. Thus, the circuit complexity can be significantly reduced again, resulting in a further cost reduction.

Preferably, the converter frequency is in a range of +/- 10% of the resonant frequency of the secondary circuit. By choosing the frequency within this range, a significant reduction of the capacitance of the first capacitor can already be achieved. The current or voltage curve is then sufficiently sinusoidal for low-loss switching.

The voltage converter may be a push-pull converter comprising at least first and second electronic switches coupled in series, wherein a first terminal of the primary inductance with the first electronic switch, a second terminal of the primary inductance with the second electronic switch and a third terminal of the primary inductance is coupled to a reference potential. Preferably, a second capacitor is connected in parallel to the primary inductance in order to limit the voltage increase and to obtain further resonance points.

According to a preferred embodiment, a third capacitor is coupled between the first and the second connection for the high-pressure discharge lamp. This serves to provide a resonance at higher frequencies for generating the take-over voltage, wherein the resonance frequency is determined by the leakage inductance of the transformer on the secondary side and the third capacitor. In operation, this third capacitor is ineffective because it is shorted by the lamp, which becomes low impedance during operation.

Particularly preferably, a first inductance is coupled between the first capacitor and the first connection for the high-pressure discharge lamp. This serves for current shaping and current limiting. It can also be used, in conjunction with the third capacitor, to set up further resonance points for the purpose of transfer voltage generation and to shift the resonance point in conjunction with the first capacitor. Under certain circumstances it makes sense to use the first inductance between the first capacitor and the first connection of the Secondary side of the transformer to couple. The third capacitor is then coupled between the junction of the first capacitor and the first inductor and the second terminal of the high pressure discharge lamp. In this case, the second capacitor blocks a part of the discharge current of the first capacitor (assuming the high-pressure discharge lamp) from the secondary side of the transformer. This reduces the flyback voltage in the primary circuit of the transformer and thus the voltage load of the first and the second electronic switch in the ignition of the high-pressure discharge lamp.

The voltage converter may also be a bridge converter comprising at least a first and a second electronic switch. In this case, the first connection of the primary inductance can be coupled to a connection point between the first and the second electronic switch, wherein the second connection of the primary inductance is coupled to the connection of the remote connection point of the second electronic switch. In this connection, a fourth capacitor can be coupled in parallel to the secondary inductance. This in turn serves to generate the transfer voltage for the high-pressure discharge lamp together with the secondary inductance of the transformer of the voltage converter.

Furthermore or alternatively, a fifth capacitor can be coupled between the connection of the connection point remote from the second electronic switch and the second connection of the primary inductance. This serves with unfavorable capacity size of the first capacitor as a balancing capacitor for the transformer and allows a shift of the resonant frequency of the entire system, because the capacitances of the first and fifth capacitors add up over the square of the transformation ratio of the transformer.

The voltage converter can also be a Einschalterwandler with an electronic switch, in particular a flyback converter represent. Preference is given to the electronic switch, a sixth capacitor connected in parallel. This serves to limit the voltage increase across the first electronic switch and also influences the resonant frequency of the secondary circuit. The inclusion of the already known from the circuit designs already described additional inductance in the secondary circuit is again possible.

Furthermore, the secondary inductance, a seventh capacitor may be connected in parallel, which in turn serves to provide the crossover frequency.

The converter frequency is at least 1 MHz in the preferred embodiments of the present invention.

Further advantageous embodiments will become apparent from the dependent claims.

The preferred embodiments presented with reference to a circuit arrangement according to the invention and their advantages, if applicable, apply correspondingly to the method according to the invention. Brief description of the drawing (s)

Fig. 1

in schematischer Darstellung ein erstes Ausführungsbeispiel einer erfindungsgemäßen Schaltungsanordnung;

Fig. 2

in schematischer Darstellung ein zweites Ausführungsbeispiel einer erfindungsgemäßen Schaltungsanordnung;

Fig. 3

in schematischer Darstellung ein drittes Ausführungsbeispiel einer erfindungsgemäßen Schaltungsanordnung; und

Fig. 4

in schematischer Darstellung ein viertes Ausführungsbeispiel einer erfindungsgemäßen Schaltungsanordnung.

Hereinafter, embodiments of the present invention will be described in more detail with reference to the accompanying drawings. Show it:

Fig. 1

a schematic representation of a first embodiment of a circuit arrangement according to the invention;

Fig. 2

a schematic representation of a second embodiment of a circuit arrangement according to the invention;

Fig. 3

a schematic representation of a third embodiment of a circuit arrangement according to the invention; and

Fig. 4

in a schematic representation of a fourth embodiment of a circuit arrangement according to the invention.

In the following exemplary embodiments, identical and identically acting components are identified by the same reference numerals.

Fig. 1 shows a schematic representation of a first embodiment of a circuit arrangement according to the invention for operating a high-pressure discharge lamp La. In this embodiment, a voltage converter 10 is realized by a push-pull converter, which comprises a first electronic switch T1 and a second electronic switch T2, which are coupled in series. The voltage converter 10 further comprises a transformer Tr having a primary inductance P1, which comprises a first partial inductance P1a and a second partial inductance P1b. A secondary inductance is S1 designated. A first terminal of the primary inductance P1 is coupled to the first electronic switch T1, while a second terminal of the primary inductance P1 is coupled to the second electronic switch T2. A third terminal, which is arranged between the first partial inductance P1a and the second partial inductance P1b, is coupled to a reference potential, which in particular represents a DC voltage U _V.

The first and second electronic switches T1, T2 are driven by a drive device 12 with a drive signal having a switching frequency f _s . On the secondary side, a first capacitor C1 is provided, which is coupled between the secondary inductance S1 and a first terminal of the high-pressure discharge lamp La. A charging device 14 coupled to the first capacitor C1 serves to charge the first capacitor C1 with a DC voltage to an ignition voltage for igniting the high-pressure discharge lamp La.

With respect to the present invention, it should be noted that inductors and capacitors generally have a frequency dependent reactance. Thus, the impedance Z of a series circuit of an ohmic resistance R, an inductance L and a capacitor C is also frequency-dependent.

In the following, R represents the ohmic resistance of the high-pressure discharge lamp La, which is usually between 10 and 200 Ω, Ls the total inductance of the secondary circuit consisting of all direct and indirect inductances, and Cs the total capacity of the secondary circuit consisting of all direct and indirect capacities: $$\left|Z\right|=\sqrt{R^2+{\left(\omega Ls-\frac{1}{\omega \mathit{Cs}}\right)}^2}$$

A direct inductance represents, for example, the additional inductance L1, while indirect inductances are formed, for example, by stray, parasitic or retroactive inductances.

A direct capacitance is, for example, the ignition or coupling capacitance C1, while indirect capacitances are formed, for example, by stray, parasitic or retroactive capacitances. The determining capacity in Cs is C1.

According to the invention, the switching frequency f _s is now chosen so that the total inductance Ls and the total capacitance Cs are operated in series resonance. To achieve this, the switching frequency f _{s should be selected} as follows: $$f_s=\frac{1}{2\pi \sqrt{\mathit{ls}*\mathit{Cs}}}$$

Values usable for the invention, however, already result in a selection of the switching frequency f _s in the range of +/- 10% of the above-indicated resonant frequency f _{s of} the secondary circuit.

Without series resonance, the impedance of the capacitor C1 would be: $$\left|Zc\right|=1/\omega C1$$

So it would be a much higher frequency or a larger capacitor necessary to a corresponding current I = U / | Z | to flow.

Fig. 2 shows a second embodiment of a circuit arrangement according to the invention, in which the primary inductance P1, a capacitor C2 is connected in parallel. This capacitor C2 serves to limit the voltage increase in the primary circuit and to provide further resonance points.

Furthermore, in the in Fig. 2 illustrated embodiment of the high pressure discharge lamp La a capacitor C3 connected in parallel. This has the task of providing a further resonance point for generating the transfer voltage.

An inductor L1 coupled between the capacitor C1 and the first terminal for the high-pressure discharge lamp La serves for current shaping and current limiting. It can also be used, in conjunction with the capacitor C3, to set up further resonance points for the purpose of transfer voltage generation and to shift the resonance point in connection with the capacitor C1. Under certain circumstances, it is also useful to couple the inductance L1 between the capacitor C1 and the first terminal of the secondary side of the transformer Tr. The capacitor C3 is then coupled between the junction of the capacitor C1 and the inductor L1 and the second terminal of the high pressure discharge lamp La. In this case, the capacitor C2 blocks a part of the discharge current of the capacitor C1 (assuming the high-pressure discharge lamp) from the secondary side of the transformer Tr from. This reduces the flyback voltage in the primary circuit of the transformer Tr and thus the voltage load of the switches T1 and T2 in the ignition of the high-pressure discharge lamp.

At the in Fig. 3 1, the voltage converter 10 represents a bridge converter, in particular a half-bridge converter, wherein the first terminal of the primary inductance P1 is coupled to a connection point between the first T1 and the second electronic switch T2. The second terminal of the primary inductance P1 is coupled to the remote from the connection point P terminal of the second electronic switch T2. Parallel to the secondary inductance, a capacitor C4 is coupled, which as well as in Fig. 2 shown capacitor C3 is the voltage overshoot of the conducive for ignition AC voltage component or for increasing the transfer voltage.

Between the remote from the connection point P terminal of the second electronic switch T2 and the second terminal of the primary inductor, a capacitor C5 is coupled. This serves as a coupling capacitor.

Fig. 4 shows an embodiment with a turn-on as a voltage converter, in the present case, a flyback converter was selected. In this case, the electronic switch T1, a capacitor C6 is connected in parallel. This serves to limit the voltage increase across the switch T1 and also influences the resonant frequency of the secondary circuit. Furthermore, the secondary inductance S1 can be connected in parallel with a capacitor C7 be the same function as the capacitor C4 in the in Fig. 3 illustrated embodiment.

In a preferred embodiment according to Fig. 1 the capacitance of the capacitor C1 is 1.5 nF. This represents about one-fifth of the capacitance C1 required for the non-resonant operation of the secondary circuit. The switching frequency is 1.2 MHz. For the ignition of the lamp, the capacitor C1 is DC charged to about 10 kV, that is, the open circuit voltage of the transformer Tr is DC raised to ignite the lamp. Thereafter, the capacitor C1 operates as a series resonant capacitor for the secondary circuit. Due to the resonance mode results in a capacitor capacity, which corresponds to the required dielectric strength of a commercially available device and geometrically without difficulty even in the smallest available space, for example, in the base of a D3 lamp fits.

Due to the resonant operation, the transistors switch off, even without the usual resonant capacitor in the primary circuit. The lamp current I is similar to sine.

Claims (15)

1. Circuit arrangement for operating at least one high-pressure discharge lamp (La) comprising

   - a voltage converter (10) comprising at least one electronic switch (T1; T2);

   - an actuation circuit (12) for actuating the at least one electronic switch (T1; T2) of the voltage converter (10) at a presettable converter frequency (f_s);

   - a first and a second connection for coupling to the at least one high-pressure discharge lamp (La);

   - a first capacitor (C1) which is coupled between the voltage converter (10) and the first connection for the discharge lamp; and

   - a charging apparatus (14), which is coupled to the first capacitor (C1) in order to charge said capacitor with a DC voltage to a starting voltage for starting the high-pressure discharge lamp (La);
   wherein the voltage converter (10) comprises a transformer (Tr), wherein the transformer (Tr) comprises a primary inductance (P1; P1a, P1b) having at least one first and one second connection and a secondary inductance (S1) having a first and a second connection,
   wherein the first capacitor (C1) is coupled between the first connection of the secondary inductance (S1) and the first connection for the at least one high-pressure discharge lamp (La),
   characterized
   in that the converter frequency (f_s) is selected during steady-state operation of the circuit arrangement in such a way that the secondary side, which at least comprises the series circuit comprising the secondary inductance (S1), the first capacitor (C1) and the high-pressure discharge lamp (La), is operated substantially at resonance.
2. Circuit arrangement according to Claim 1,
   characterized
   in that the converter frequency (f_s) is in a range of +/- 10% of the resonant frequency of the secondary circuit.
3. Circuit arrangement according to either of Claims 1 and 2,
   characterized
   in that the voltage converter (10) is a push-pull converter, which comprises at least one first electronic switch (T1) and one second electronic switch (T2), which are coupled in series, wherein a first connection of the primary inductance (P1; P1a, P1b) is coupled to the first electronic switch (T1) a second connection of the primary inductance (P1; P1a, P1b) is coupled to the second electronic switch (T2), and a third connection of the primary inductance (P1; P1a, P1b) is coupled to a reference potential (U_V).
4. Circuit arrangement according to Claim 3,
   characterized
   in that a second capacitor (C2) is connected in parallel with the primary inductance (P1; P1a, P1b).
5. Circuit arrangement according to either of Claims 3 and 4,
   characterized
   in that a third capacitor (C3) is coupled between the first and second connections for the high-pressure discharge lamp (La).
6. Circuit arrangement according to one of Claims 3 to 5,
   characterized
   in that a first inductance (L1) is coupled between the first capacitor (C1) and the first connection for the high-pressure discharge lamp (La).
7. Circuit arrangement according to one of Claims 1 to 3,
   characterized
   in that the voltage converter (10) is a bridge converter, which comprises at least one first electronic switch (T1) and one second electronic switch (T2).
8. Circuit arrangement according to Claim 7,
   characterized
   in that the first connection of the primary inductance (P1; P1a, P1b) is coupled to a node (P) between the first electronic switch (T1) and the second electronic switch (T2), wherein the second connection of the primary inductance (P1; P1a, P1b) is coupled to that connection of the second electronic switch (T2) which is remote from the node (P).
9. Circuit arrangement according to either of Claims 7 and 8,
   characterized
   in that a fourth capacitor (C4) is coupled in parallel with the secondary inductance (S1).
10. Circuit arrangement according to one of Claims 7 to 9,
    characterized
    in that a fifth capacitor (C5) is coupled between that connection of the electronic switch (T2) which is remote from the node (P) and the second connection of the primary inductance (P1; P1a, P1b).
11. Circuit arrangement according to one of the preceding claims,
    characterized
    in that the voltage converter (10) is an on-off switch converter comprising an electronic switch (T1), in particular a flyback converter.
12. Circuit arrangement according to Claim 11,
    characterized
    in that a sixth capacitor (C6) is connected in parallel with the electronic switch (T1).
13. Circuit arrangement according to either of Claims 11 and 12,
    characterized
    in that a seventh capacitor (C7) is connected in parallel with the secondary inductance (S1).
14. Circuit arrangement according to one of the preceding claims,
    characterized
    in that the converter frequency (f_s) is at least 1 MHz.
15. Method for operating at least one high-pressure discharge lamp (La) using a circuit arrangement comprising a voltage converter (10) comprising at least one electronic switch (T1; T2); an actuation circuit (12) for actuating the at least one electronic switch (T1; T2) of the voltage converter (10) at a presettable converter frequency (f_s); a first and a second connection for coupling to the at least one high-pressure discharge lamp (La); a first capacitor (C1), which is coupled between the voltage converter (10) and the first connection for the discharge lamp; and a charging apparatus (14), which is coupled to the first capacitor (C1) in order to charge said capacitor with a DC voltage to a starting voltage for starting the high-pressure discharge lamp (La);
    characterized by the following steps:

    a) providing a transformer (Tr) having a primary inductance (P1; P1a, P1b), which comprises at least one first and one second connection, and a secondary inductance (S1), which comprises a first and a second connection;

    b) coupling the first capacitor (C1) between the first connection of the secondary inductance (S1) and the first connection for the at least one high-pressure discharge lamp (La); and

    c) actuating the at least one electronic switch (T1; T2) of the voltage converter (10) during steady-state operation of the circuit arrangement at a converter frequency (f_s) in such a way that the secondary side, which comprises at least the series circuit comprising the secondary inductance (S1), the first capacitor (C1) and the high-pressure discharge lamp (La), is operated substantially at resonance.

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